Patent GB-1194876-A (GB)
Title: Speed Programmed Friction Welding
Inventor: FARMER CHARLES GENE
IPC: B23K20/12
Filed: 1967-07-24
Abstract: 1,194,876. Welding by pressure. CATERPILLAR TRACTOR CO. 24 July, 1967 [29 July, 1966], No. 33982/67. Heading B3R. A machine for friction welding workpieces comprises loading means for pressing the workpieces together, variable speed drive means for rotating one workpiece with respect to the other and speed programming means for producing a predetermined variation of the relative rotational speed of the one workpiece with time and for controlling the relative rotational speed throughout the entire welding period. A machine includes a stationary chuck 24, Fig. 1, on a slide 26 and a rotatable chuck 23 with variable speed drive means therefor including an electric motor 28, a hydrostatic pump 29 and a hydrostatic motor 31, the pump being driven by the motor 28 to supply pressurized fluid to the motor 31 which drives the chuck 23 by a shaft 33. The speed of the motor 31 is determined by the angular position of a cam 34 in the motor and a cam 36 in the pump, the position of the cam 34 being set by a hydraulically actuated control 37 and the position of the cam 36 being set by control 38. Rectilinear potentiometers 39, 41 form sensing units to sense the positions of the cams 34, 36. A tachometer generator 42 generates a signal corresponding to the rotational speed of the shaft 33. The slide 26 is moved to bring the workpieces into contact by an hydraulic piston-cylinder device 27 and the pressure exerted thereby is programmed by means which includes a timer and solenoid operated valves to cause the device 27 to exert a desired initial load and after a desired time to to exert an increased load, the load being removed when the weld is completed. Speed programming means 71, Fig. 5, includes a programmer 72 and a controller 73. The programmer 72 is electrical and includes a diode function generator and a time generator but may be cam surfaces, tapes or punched cards and generates a desired speed signal while the controller 73 forces the output speed of the shaft 33 to equal the programmed speed. The controller includes electro-hydraulic servo valves 74, 76 which control the flow of pressure fluid from a pump 77 to the displacement controls 38, 37 and the speed signal from the programmer is supplied to the valves 74, 76 through lines 82, 83. The hydraulic circuit for the pump 29 and motor 31 includes relief valve 87, replenishing pump 89 and check valve 91. The speed programming means is a closed loop which includes feedback means for comparing the actual speed with the programmed speed. In operation the desired speed-time relationship is programmed into programmer 72, the pressure programming means are programmed, the electric motor accelerates the pump 29 and motor 31 and cylinder 27 causes the workpieces to engage; the load on the workpieces and the relative speed being maintained at the programmed levels. In a modified apparatus the hydrostatic pump 29 and motor 31 are arranged end to end and only a single displacement control is required. The pump and motor can be used as a brake to absorb excess energy when small parts are being welded-the displacement cam in the pump being reversed so that the motor acts as a pump and the pump as a motor or the drive shaft 33 may be allowed to freewheel. The programmed speed time curve may be as shown in Fig. 12, which is a curve characteristic of an intertial weld using a large flywheel at low initial velocity. Other speed curves are shown including one which shows a period of heating, a period of forging, a further period of heating and a final forging step. Instead of the hydrostatic drive a planetary type of power shift transmission programmed to shift under power from a high speed to a lower speed may be used. A further modified apparatus is similar to that of Fig. 1, but includes a flywheel freely mounted for rotation on the shaft 33 but by a one way clutch being capable of being connected to the shaft. In operation an hydraulic cylinder is actuated to clutch a splined collar on the shaft to the flywheel during a portion of the time the shaft is being accelerated to the desired initial speed and when the desired amount of energy is stored in the flywheel it is disconnected from the splined collar to freewheel on the shaft. After the parts have been engaged and the speed has dropped into the forging range the clutch connects the flywheel to the shaft to assist in the forging part of the cycle. A modified drive for a speed programmed machine includes a fixed displacement pump driven by an electric motor or an I.C. engine to supply fluid to an hydraulic motor driving the output shaft of the machine. The motor speed is determined by the amount of fluid supplied through an. electrohydraulic servo valve whose position is controlled by a programmer.